A valve device, which is composed of a rotary type valve, is known in the art and practically used, for example, as disclosed in Japanese Patent Publication No. 2002-327851.
A rotary type valve having the following structure is generally used in the valve device. The rotary type valve is composed of a valve housing having multiple fluid ports and a cylindrical valve member movably accommodated in the valve housing for respectively opening and closing the fluid ports. In the above rotary type valve, the valve member is rotated so as to increase or decrease an opening area (or a fluid flow passage area), which is formed by a fluid port of the valve member (a valve-side fluid port) and a fluid port of the valve housing (a housing-side fluid port).
A cooling fluid control system is installed in an automotive vehicle, which is propelled by an internal combustion engine (hereinafter, the engine), wherein multiple fluid passages are provided for the purpose of effectively using cooling water of the engine. A valve device having a rotary type valve is incorporated into the cooling fluid control system so as to open and close each of the multiple fluid passages. The valve device is composed of a complex type valve device, which has multiple rotary type valves and multiple actuators, each of which is attached to the respective rotary type valve for properly operating the rotary type valve in order to achieve a variety of valve operation modes.
In recent years, a number of equipment, in particular, a number of devices to be mounted in an engine room of the vehicle is increased in accordance with developments of the vehicle, in order to meet various kinds of requirements in view of improving engine performance, occupant comfort and so on. It is, therefore, strictly required for those equipment and devices to realize reduction in size and weight. Accordingly, it becomes more and more difficult that the valve device having the above complex structure is smoothly mounted in the engine room. It is, therefore, necessary to realize the reduction in size and weight for the valve device.
A valve device having a multi-stage structure is proposed in the art as one of countermeasures for reducing the size and the weight of the valve device. In the multi-stage structure, multiple valve portions of a rotary type are arranged in an axial direction of a valve member in order that one actuator for rotating the valve member is commonly used for each of the multiple valve portions. In other words, a valve device, which has one valve member of the rotary type and one actuator for driving the valve member, is proposed. However, such a valve device is not sufficiently reduced in the size and the weight. Therefore, it is necessary for the valve device to further improve the reduction of the size and the weight.
According to the study of the inventor of the present disclosure, there are still following problems in the above valve device having the multiple-stage structure, so long as a basic structure of the rotary type valve device is continuously used:
(1) In the rotary type valve device, the valve member of the cylindrical shape is rotated so as to increase or decrease the opening area of the fluid port. When the valve member is simply made longer in its axial direction and the multiple valve portions are arranged in the axial direction so as to provide the multi-stage valve structure, an outer shape of the valve device inevitably becomes larger. In addition, it is correspondingly necessary to provide a larger actuator in order to rotate the valve member of the rotary type, the outer shape of which has become larger.
(2) In the rotary type valve device, it is necessary to carry out a desired multi-stage opening-closing control during the valve member of the cylindrical shape is rotated by one rotation (360°). Therefore, an effective rotational angle is restricted in each of the valve portions formed in each of the multiple stages, depending on a number of the multiple stages. It becomes necessary to form a larger fluid port in each of the valve portions when a desired amount of the flow rate is obtained in the restricted rotational angle. In other words, it is necessary to provide a larger valve member and a larger valve housing in order to sufficiently obtain a fluid flow area by enlarging the fluid port. As a result, the valve device may become larger as a whole.
(3) According to the above prior art (JP 2002-327851), the fluid port is formed in an oval shape, wherein a length of the oval shape in a rotational axis direction of the valve member is made to be longer than a length in a direction perpendicular to the rotational axis direction. However, it is not sufficient for the valve device of the above prior art to satisfy requirements for reduction in the size and the weight.
(4) The inventor of the present disclosure further investigated the shape of the fluid ports, an arrangement of the fluid passages in the multi-stage structure and so on, in order to make dimensions of the valve device smaller in the axial direction and in the radial direction. In other words, the inventor worked in research and development in order to make smaller the size and the weight of the valve device, without largely changing the basic mechanism of the rotary type valve device.